I have a large file backup tar file (142 GB). When i run the restore command, it completes successfully but no changes are applied to the instance - the repo dir (/var/opt/gitlab/git-data/repositories) is empty.

Add --trace to the backup command and run it in nohup and capture the log you can see more detailed trace of what is happening in the background and where it is failing.
Your command will look like this

[root@localhost ~]# nohup sudo gitlab-rake gitlab:backup:restore BACKUP=1472232253 --trace &
press enter/return after this command.[root@localhost ~]# tail -f nohup.out
During large backup restore operations you might face this Issue. Try this and see if it works.